It is a longstanding requirement of the textiles industry that substrates used in apparel manufacture, such as fabrics and fibers for clothing, exhibit special properties that persist through numerous washings. One such special property of increasing interest is antibacterial and antifungal performance. Antibacterial and/or antifungal effects are typically achieved by loading the fabric substrate with a biocide or fungicide that is released under a certain set of environmental conditions. For most inorganic biocides, such as silver and copper, water based corrosion is the primary method for the release of metal ions responsible for killing microbes and/or fungi. Consequently, the provision of antimicrobial performance with wash-durability is difficult to achieve because washing conditions accelerate the release of water-soluble antimicrobial and antifungal agents. If release of antimicrobial or antifungal agent occurs too quickly or there is an insufficient “reservoir” of the agent, the fabric will be depleted prematurely, leaving the fabric substrate unprotected from infestation.
The related art is characterized by a variety of inorganic agents, mainly zeolites and metal particles that release antimicrobial or antifungal metal ions such as Ag+, Zn2+, Cu2+. One general approach for manufacturing fabric substrates laden with inorganic agent involves methods such as soak or pad application to fabric substrates after they have been woven. Alternatively, inorganic agents could be mixed with polymers and extruded into fibers, although known extrusion attempts to date are rife with problems, such as inconsistent concentration and dispersion of the antimicrobial agent, especially in the case of metal particles, which tend to fall out of solution and may clump together during manufacturing, application, and/or use, thereby rendering an undesirable textile product having inadequate, uncontrolled, and/or non-durable antimicrobial activity, as well as defects such as weak tensile strength, high abrasiveness, and other undesirable properties.
Zeolite-based antimicrobial agents are widely used due to their low cost and colorless nature. Yet there are drawbacks to their use. The weight fraction of active ingredient tends to be very low (<5%) so the majority of additive is zeolite carrier. When used in textiles, the carrier can negatively impact the mechanical property of extruded fibers. Furthermore, the zeolite particles tend to be micron size, which limits the denier size of extrudable fiber, making the manufacture of fibers, such as microfibers, very difficult. Additionally, aqueous sodium ions accelerate the release of silver ions in zeolites, which occurs through ion exchange. Therefore, the durability of fabric substrates treated with zeolite agents is limited when washed in hard water wherein sodium ions are commonly exchanged for calcium ions by water softeners, or when contacted with salt solutions, such as human sweat and ocean water. Lastly, silver ions in the inner part of zeolite carrier particles may not be able to diffuse out of the carrier, rendering a fraction of the silver undeliverable and therefore ineffective as an antimicrobial and/or antifungal agent.
The use of metallic nanoparticles as antimicrobial and antifungal agents in textiles has been attempted, but success has been elusive due to clumping and other challenges to obtaining a controlled, uniform dispersion and concentration of the nanoparticles in the final textile product. Theoretically, the high surface area of nanoparticles offers an advantage over micron size antimicrobial and/or antifungal agents due to the nature of the ion release mechanism. The release mechanism involves hydromediated oxidation and dissolution of the metal surface, which consequently exposes a fresh metal. Furthermore, since the entire particle is metal, it can eventually be reduced to ions, and therefore serves as highly efficient antimicrobial and/or antifungal agent reservoir. Despite these advantages, metal nanoparticles have not been successfully incorporated into textiles to produce a product having desirable properties including durable antibacterial and/or antifungal biocidal activity after repeated use and washings.
For all these reasons, there exists a continuing and unmet need for improved textiles having antimicrobial and/or antifungal agents and for improved methods for their manufacture.